For most users, hosting a server is unnecessary. The PPSSPP community maintains active public Adhoc servers.
If you want to play with someone over the internet, you need a public relay. All players must enter the exact same server address in their Networking settings. adhoc server ppsspp
It takes the local wireless signals and routes them through the internet. If you can run the emulator, you can run this server. For most users, hosting a server is unnecessary